The present invention relates to a horizontal frequency signal driving circuit for a CRT apparatus and more particularly to a multi-horizontal frequency signal driving circuit which can drive a flyback transformer for generating a stabilized high voltage in response to a signal having various frequencies.
In a conventional horizontal frequency signal driving circuit, a relay or an analog switch has been optionally used in the input stage of the circuit for selectively processing the various frequencies. Now, assume that the next stage of the circuit is a conventional horizontal deflection circuit. Then, the following problem arises. As is well known, in a conventional horizontal deflection circuit, an input signal, i.e., a horizontal synchronization signal is processed through a horizontal oscillation circuit, a horizontal driving circuit and a horizontal output circuit, and the resultant voltage signal is supplied to one terminal of the primary coil of a flyback transformer (FBT) for generating a high voltage which will be supplied to an anode of a CRT. Connected to the other terminal of the primary coil of the FBT is a DC voltage power supply. In the case where the frequency of the input signal is changed, the oscillating frequency of the horizontal oscillation circuit and, hence, the supply voltage to the FBT are also changed to stabilize the high voltage output from the FBT. In this case, however, since the change of the frequency of the input signal is performed by a switching operation of a relay or an analog switch, the oscillating frequency and, hence, the supply voltage to the FBT may be unstabilized at the time of the switching point. Thus, at this point, the high voltage output from the FBT may be raised or lowered from a predetermined level. This has an adverse effect on the CRT display.